The spread of high performance mobile terminals such as smart phones has brought about an increase (explosion) of traffic in a mobile communication network. It becomes necessary to increase or extend network facilities in order to cope with a shortage of network band, decrease in response, or the like due to an increase in the number of terminals using the network, increase of traffics, and so forth. For this reason, various methods of achieving cost reduction by offloading a traffic to a different network have been proposed.
In LIPA (Local IP Access), as specified in 3GPP (3rd Generation Partnership Project) specifications, for example, a traffic between a mobile terminal UE (User Equipment) and a host on a private network (e.g., a home network) such as an in-house LAN (Local Area network), an enterprise network, or the like) connected to a base station (H(e)NB) such as a femtocell or a home cell is not forwarded to a core network. Instead, the traffic is offloaded from the H(e)NB to the private network through a local gateway (L-GW) (see Section 5.2.3 in Non Patent Literature 1). The H(e)NB represents an HNB (Home Node B) or an HeNB (Home-evolved Node B).
In SIPTO (Selected IP Traffic Offload) in the 3GPP specifications, traffic associated with a specific APN (Access Point Name) or a specific application can be set to offloading target. Alternatively, offload control can be performed, based on a destination IP (Internet Protocol) address.
In SIPTO solution 4 (see Section 5.5 in Non Patent Literature 1), a configuration as illustrated in FIG. 19 is disclosed as SIPTO to be applied to UMTS (Universal Mobile Telecommunication Systems) macrocell and HNB subsystem (femtocell). As illustrated in FIG. 19, there is a provided TOF (Traffic Offload) between an RNC (Radio Network Controller)/HNB and an SGSN (Serving GPRS (General Packet Radio System) Support Node). The TOF interfaces via a Gi subset with the Internet. FIG. 19 is a diagram based on FIG. 5.5.2.1 in Non Patent Literature 1. Referring to FIG. 19, the TOF is provided on Iu-PS, and provides a standard Iu-PS interface to the RNC and the SGSN. Iu is an interface between the RNC and a core network (MSC (mobile Switching Center: mobile switching station) or the SGSN), while the Iu-PS is an interface between the RNC and a packet (Packet Switched) core network. Gi is an interface between a GGSN (Gateway GPRS Support Node) and a PDN (Packet Data Network).
The TOF on the Iu-PS performs message inspection of a NAS (Non Access Stratum: non access stratum)/RANAP (Radio Access Network Application Part) message, obtains subscriber information, and then establishes a local UE offload context. Further, the TOF obtains PDP (Packet Data Protocol) context information, and establishes a local session offload context. The TOF determines whether or not to perform offloading during attach and PDP activation procedure, for example, based on the above-mentioned information. When the offloading is performed, the TOF extracts uplink traffic from a GTP-U (GPRS Tunneling Protocol for User plane) tunnel (tunnel between a UE and the GGSN) and executes NAT (Network Address Translation) using a NAT (Network Address Translation) gateway or the like, for example, thereby offloading the traffic. For the NAT, address translation from a private IP address to a global IP address is performed by a router or the like. Alternatively, a set of the IP address and a TCP (transmission control protocol)/UDP (user datagram protocol) port number is translated. The TOF further performs reverse NAT on downlink offload traffic and returns the downlink offload traffic by inserting the downlink offload traffic to the GTP-U tunnel.
In this manner, in the SIPTO solution 4, offloading is determined, based on a user, an APN, a service type, an IP address, and so forth, using packet inspection and NAT. Data traffic is offloaded on the Iu-PS interface that is an interface (user plane) between RNC and SGSN. For LTE (Long Term Evolution), addition of a local packet data network gateway (L-PGW (PDN (Packet Data Network) Gateway)) is necessary.
SIPTO solution 5 (see Section 5.6 in Non Patent Literature 1) can accommodate a macrocell, an HNB, and both of UMTS and the LTE (and further can accommodate a UE supporting or not supporting a plurality of PDN connections). Connection to the Internet or the like is performed through an L-PGW (L-GGSN) connected to a serving gateway SGW (RNC) (see FIG. 5.6.3.2, 5.6.3.3, and 5.6.3.4 in Non Patent Literature 1). SGW may be also denoted as S-GW.
Alternatively, a traffic may be offloaded to a different network. A mobile terminal such as a smart phone, a tablet terminal, or the like equipped with a Wi-Fi (Wireless Fidelity) connection function is connected to the Internet by a Wi-Fi access point or the like, or a wireless LAN (Wireless Local Area Network) or the like (this offloading is also referred to as Wi-Fi offloading). In this case, when a mobile terminal (UE) leaves a location where the Wi-Fi access point is installed, communication connection cannot be made. That is, there is a problem with connectivity and security when the mobile terminal (UE) moves. There is also a configuration in which the wireless LAN is connected to a PDN through a PGW (PDN Gateway: also denoted as P-GW) and a GGSN (see Section 4.2 in Non Patent Literature 2).